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Abstract:

A current path in an installation switching device includes first and
second contact points, which respectively include first and second
levers. The second lever is arranged in an air gap in a magnetic circuit.
In case of a short circuit, an electrodynamic force, which leads to rapid
opening of the second contact point, can act on the second lever due to
interaction of current flow with magnetic flux within the air gap. A
switching mechanism acts via a first connecting line on the first lever
to open and/or keep open the first contact point. In case of overcurrent
tripping, an overcurrent release acts through the switching mechanism and
a second connecting line on the switching mechanism to open and keep open
the first contact point. In case of short-circuit tripping, the second
lever acts via a third connecting line on the switching mechanism to keep
the first contact point open.

Claims:

1. An electrical installation switching device comprising: a housing; a
current path which runs in the housing between a first connecting point
and a second connecting point; at least one first contact point including
a first contact lever, the at least one contact point being configured to
at least one of open and close the current path; an electromagnetic
short-circuit current release including a magnetic circuit with an air
gap; an overcurrent release including a switching mechanism operating
element which is configured to change from a rest position to a trip
position when overcurrent tripping occurs; and a switching mechanism
including a tripping lever and a striking lever which is configured to be
pivoted between a rest position and a trip position, wherein the current
path includes at least one second contact point which includes a second
contact lever, wherein the second contact lever is arranged at least
partially in the air gap in the magnetic circuit to cause, in the event
of a short circuit, an electrodynamic force, which leads to rapid opening
of the at least one second contact point, to act on the second contact
lever due to interaction of flow of current in the current path with
magnetic flux within the air gap, wherein the switching mechanism is
configured to act, via a first operating connecting line, on the first
contact lever to at least one of open the first contact point and keep
the first contact point open, wherein, in the event of overcurrent
tripping, the overcurrent release is configured to act through the
switching mechanism and via a second operating connecting line on the
switching mechanism to open the first contact point and keep the first
contact point open, and wherein, in the event of short-circuit tripping,
the second contact lever is configured to act, via a third operating
connecting line, on the switching mechanism to keep the first contact
point open.

2. The electrical installation switching device according to claim 1,
comprising: a first coupling rod configured to couple the switching
mechanism operating element to the tripping lever.

3. The electrical installation switching device according to claim 2,
wherein the switching mechanism operating element includes at its free
end a control cam body which has a control cam, and wherein the first
coupling rod, which is supported at a first end on the control cam, is
pressed by its second end against the tripping lever when the switching
mechanism operating element moves to the trip position.

4. The electrical installation switching device according to claim 2,
wherein the switching mechanism operating element comprises a shaft which
is borne to be rotatable about its longitudinal axis.

5. The electrical installation switching device according to claim 1,
wherein the first contact piece includes a first stationary contact
piece, and wherein the installation switching device comprises a first
contact compression spring configured to apply a resetting force to act
on the first contact lever in a direction of the first contact piece.

6. The electrical installation switching device according to claim 1,
wherein the first contact piece includes a first stationary contact
piece, and the second contact piece includes a second stationary contact
piece, wherein the second contact lever is in the form of a moving
contact link which includes two moving contact pieces which are
configured to interact with the first and second stationary contact
pieces to form a double contact point, and wherein the installation
switching device comprises a second contact compression spring configured
to apply a resetting force to act on the second contact lever in a
direction of the stationary contact pieces.

7. The electrical installation switching device according to claim 6,
comprising: a second coupling rod configured to couple the moving contact
link to the striking lever of the switching mechanism.

8. The electrical installation switching device according to claim 7,
wherein the second coupling rod is configured to transmit a linear
movement of the moving contact link during opening of the second contact
point to a free end of the striking lever, and cause the striking lever
to pivot.

9. The electrical installation switching device according to claim 1,
wherein the first contact point, the short-circuit current release and
the overcurrent release are arranged one behind the other in the housing
in a flow direction of current through the current path.

10. The electrical installation switching device according to claim 9,
wherein the housing has an essentially cuboid shape including a front
narrow face, a rear narrow face, an upper longitudinal face, and a lower
longitudinal face, wherein the front narrow face includes an operating
lever for manual operation of the switching mechanism, and wherein the
short-circuit current release and the overcurrent release are connected
to the switching mechanism, which is arranged on the front narrow face.

11. The electrical installation switching device according to claim 10,
wherein the first connecting point is in the form of a connecting plate
for screwing to a contact rail.

12. The electrical installation switching device according to claim 1,
comprising: an overcurrent magnetic circuit to which the switching
mechanism operating element of the overcurrent release is coupled; and
wherein the force which acts on the switching mechanism operating element
is produced by a magnetic field of the overcurrent, wherein the switching
mechanism operating element is coupled to an electromagnetic damping
element to set a tripping delay time, and wherein the switching mechanism
operating element is coupled to a setting element to set an overcurrent
tripping threshold.

13. The electrical installation switching device according to claim 3,
wherein the first contact piece includes a first stationary contact
piece, and wherein the installation switching device comprises a first
contact compression spring configured to apply a resetting force to act
on the first contact lever in a direction of the first contact piece.

14. The electrical installation switching device according to claim 5,
wherein the second contact piece includes a second stationary contact
piece, wherein the second contact lever is in the form of a moving
contact link which includes two moving contact pieces which are
configured to interact with the first and second stationary contact
pieces to form a double contact point, and wherein the installation
switching device comprises a second contact compression spring configured
to apply a resetting force to act on the second contact lever in a
direction of the stationary contact pieces.

15. The electrical installation switching device according to claim 14,
comprising: a second coupling rod configured to couple the moving contact
link to the striking lever of the switching mechanism.

16. The electrical installation switching device according to claim 15,
wherein the second coupling rod is configured to transmit a linear
movement of the moving contact link during opening of the second contact
point to a free end of the striking lever, and cause the striking lever
to pivot.

Description:

RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. §119 to
German Patent Application No. 10 2011 008 829.6 filed in Germany on Jan.
19, 2011, the entire content of which is hereby incorporated by reference
in its entirety.

FIELD

[0002] The present disclosure relates to an electrical installation
switching device. More particularly, the present disclosure relates an
installation switching device which achieves a fast and reliable
disconnection of short-circuit current, and to such an installation
switching device which can be installed in a 19-inch rack insert.

[0004] By way of example, one circuit breaker of this type is disclosed in
DE 10 2008 006 863 A1. In a circuit breaker such as this, a short-circuit
current is disconnected with the aid of an impact-type armature. The
field of a magnet coil, through which the current flows, excites the
magnetic circuit within the electromagnetic short-circuit current
release, and the impact-type armature is thus moved by electrodynamic
interaction. The impact-type armature is coupled to a striking pin which
strikes the contact lever such that the contact point is opened, and
which at the same time acts on the switching mechanism, leading to
unlatching of the switching mechanism and therefore to the contact point
being kept permanently open, until the switching mechanism is latched
again, only after which can the contact point be closed again.

[0005] In known installation switching devices, overcurrent tripping takes
place with the aid of a thermomechanical tripping element, generally a
thermal bimetallic strip. The overcurrent causes heating of the thermal
bimetallic strip, resulting in the strip bending. In the bent state, the
thermal bimetallic strip unlatches the switching mechanism by an
appropriate link by means of a switching mechanism operating element, in
response to which the contact point is likewise permanently opened until
the switching mechanism is latched again, only after which can the
contact point be closed again.

[0006] The switching mechanism disclosed in DE 10 2008 006 863 A1 has a
latching point which is formed between a tripping lever and a latching
lever. In addition, an intermediate lever is provided, which interacts
with a contact lever. Furthermore, a switching handle is provided, which
is coupled via a bracket to the intermediate lever, with the intermediate
lever being mounted such that it can move relative to the latching lever.
When the latching point is latched, a rigid lever chain is formed from
the switching handle via the bracket and the intermediate lever to the
contact lever. When the latching point is unlatched, the rigid coupling
collapses and the intermediate lever can be moved relative to the
latching lever. The latching point can be unlatched by acting on the
tripping lever in order to pivot it such that the latching point is
unlatched. For this purpose, DE 10 2008 006 863 A1 provides a striking
lever, which acts on the tripping lever when it pivots, and pivots the
tripping lever in order to unlatch the latching point. The impact-type
armature of the magnetic short-circuit current release and the thermal
bimetallic strip of the overcurrent release both act on the striking
lever, and the tripping lever is moved indirectly via the striking lever
to its unlatched position.

[0007] In known installation switching devices, the response rate of the
magnetic release is limited, since it includes a plurality of mechanical
subsystems, each of which has a certain amount of mechanical inertia. The
current limiting in the event of a short circuit is therefore also
limited. Furthermore, in known installation switching devices,
temperature compensation is required for the overcurrent release.

[0008] For fitting, known circuit breakers are normally mounted on a
top-hat rail by means of a quick-release attachment. For electrical
protection of telecommunications facilities, a circuit breaker for DC
applications is often used, with very fast short-circuit disconnection
and overcurrent tripping independently of the temperature. When used in
switchgear cabinets, for example for telecommunications infrastructure,
19-inch rack inserts with a specific height are often used. This height
has a subdivision unit of 1 U, approximately 44.45 mm. Switching devices
for use in these switchgear cabinets should not exceed a height of 1 U.
In addition, the switching device should make direct contact with and be
mounted on a copper rail. The normal physical size of known circuit
breakers therefore cannot be used.

SUMMARY

[0009] An exemplary embodiment of the present disclosure provides an
electrical installation switching device which includes a housing, and a
current path which runs in the housing between a first connecting point
and a second connecting point. The exemplary installation switching
device also includes at least one first contact point including a first
contact lever, where the at least one contact point is configured to at
least one of open and close the current path. The exemplary installation
switching device also includes an electromagnetic short-circuit current
release having a magnetic circuit with an air gap. In addition, the
exemplary installation switching device includes an overcurrent release
having a switching mechanism operating element which is configured to
change from a rest position to a trip position when overcurrent tripping
occurs. Furthermore, the exemplary installation switching device includes
a switching mechanism including a tripping lever and a striking lever
which is configured to be pivoted between a rest position and a trip
position. The current path includes at least one second contact point
which includes a second contact lever. The second contact lever is
arranged at least partially in the air gap in the magnetic circuit to
cause, in the event of a short circuit, an electrodynamic force, which
leads to rapid opening of the at least one second contact point, to act
on the second contact lever due to interaction of flow of current in the
current path with magnetic flux within the air gap. The switching
mechanism is configured to act, via a first operating connecting line, on
the first contact lever to at least one of open the first contact point
and keep the first contact point open. In the event of overcurrent
tripping, the overcurrent release is configured to act through the
switching mechanism and via a second operating connecting line on the
switching mechanism to open the first contact point and keep the first
contact point open. In the event of short-circuit tripping, the second
contact lever is configured to act, via a third operating connecting
line, on the switching mechanism to keep the first contact point open.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Additional refinements, advantages and features of the present
disclosure are described in more detail below with reference to exemplary
embodiments illustrated in the drawings, in which:

[0011]FIG. 1 shows a schematic view of an installation switching device
according to an exemplary embodiment of the present disclosure; and

[0012]FIG. 2 shows a view into the open housing lower part of an
installation switching device according to an exemplary embodiment of the
present disclosure.

[0013] In the description of exemplary embodiments below, various
directions are described to illustrate features of the present disclosure
with reference to the orientation of the constituent elements illustrated
in the drawings. It is to be understood that the directions used in the
following description are exemplary, and the present disclosure is not
limited thereto.

DETAILED DESCRIPTION

[0014] Exemplary embodiments of the present disclosure provide an
installation switching device which achieves a faster and reliable
short-circuit current disconnection than can be achieved with known
techniques, while furthermore allowing installation of the installation
switching device in a 19-inch rack insert.

[0015] Exemplary embodiments of the present disclosure provide an
electrical installation switching device which includes a current path
which runs in a housing between a first connecting point and a second
connecting point. The circuit path is configured to be opened and closed
at at least one first contact point which includes a first contact lever.
The exemplary installation switching device also includes an
electromagnetic short-circuit current release having a magnetic circuit
with an air gap. The exemplary installation switching device also
includes an overcurrent release having a switching mechanism operating
element which changes from a rest position to a trip position when
overcurrent tripping occurs. In addition, the exemplary installation
switching device includes a switching mechanism which includes a tripping
lever as well as a striking lever which can be pivoted between a rest
position and a trip position.

[0016] In accordance with an exemplary embodiment of the present
disclosure, the current path includes at least one second contact point
which includes a second contact lever. The second contact lever is
arranged at least partially in the air gap in the magnetic circuit such
that, in the event of a short circuit, an electrodynamic force which
leads to rapid opening of the at least one second contact point can act
on the second contact lever as a result of the interaction of the current
flow with the magnetic flux within the air gap. The switching mechanism
acts via a first operating connecting line on the first contact lever in
order to open the first contact point and/or to keep it open. In the
event of overcurrent tripping, the overcurrent release acts through the
switching mechanism and via a second operating connecting line on the
switching mechanism in order to open the first contact point and keep it
open. In the event of short-circuit tripping, the second contact lever
acts via a third operating connecting line on the switching mechanism in
order to keep the first contact point open.

[0017] The installation switching device according to the disclosure uses
a switching mechanism based on that described in DE 10 2008 006 863 A1.

[0018] An installation switching device according to the present
disclosure has the advantage that short-circuit currents are disconnected
more quickly than in a known device. In the event of overcurrent
tripping, the contact point is kept open permanently after the switching
mechanism has been unlatched, where reconnection after renewed latching
of the switching mechanism, etc., is still available, in the normal
manner.

[0019] In accordance with an exemplary embodiment, the magnetic
short-circuit current tripping included in the installation switching
device according to the present disclosure advantageously provides that
the magnetic flux or field of the magnetic circuit and the second contact
lever can interact directly. This allows the second contact point to be
opened much more quickly than in the case of impact-type armature systems
as used in known circuit breakers in which, as already mentioned, the
mechanical inertia of the moving components involved limits the tripping
rate. In the case of magnetic short-circuit current tripping included in
the installation switching device according to the present disclosure, a
force which results from the force effect, which is known as the Lorentz
force, of a magnetic field on an electrical charge which is moving in the
field acts on the second contact lever. This force acts directly, without
the interposition of mechanical components such as a moving armature or
striking pin. If the second contact point has been opened quickly, the
current path is interrupted. According to an exemplary embodiment, in
order to ensure that the contact point is kept open permanently, the
second contact lever acts on the switching mechanism, which then opens
the first contact point. While the short-circuit current has been
interrupted, the magnetic force on the second contact lever will
disappear. The current path is kept open permanently via the first
contact point. This also applies during manual disconnection. In the
event of overcurrent tripping, the current path is disconnected and kept
open via the switching mechanism and the first contact point. This
ensures reliable short-circuit current and overcurrent disconnection.
According to an exemplary embodiment, the introduction of at least two
series-connected contact points in order to distribute the tasks of rapid
first disconnection and permanently keeping two different contact points
open in the event of a short circuit for the first time allows all the
required subsystems and components to be constructed in a very low
housing with the required height of 44.45 mm--this is because, in
contrast, a conventional switch has a height of at least 60 mm.

[0020] According to an exemplary embodiment of the present disclosure, the
switching mechanism operating element of the overcurrent release is
coupled to an overcurrent magnetic circuit. The force which acts on the
switching mechanism operating element is produced by the magnetic field
of the overcurrent. The switching mechanism operating element is coupled
to an electromagnetic damping element in order to set the tripping delay
time. The switching mechanism operating element is coupled to a setting
element in order to set the overcurrent tripping threshold. In this
exemplary embodiment, the overcurrent tripping can also be in the form of
a magnetic tripping system. This arrangement has the advantage that the
overcurrent tripping can be carried out independently of the temperature.
This is because, in the case of known thermal bimetallic strip releases,
the bimetallic strip is also deformed when there is a change in the
ambient temperature, as a result of which an overcurrent release such as
this generally has to be coupled to a compensation apparatus. On the
contrary, the magnetic overcurrent release used in the installation
switching device according to the present disclosure is not dependent on
the temperature.

[0021] According to an exemplary embodiment of the present disclosure, the
housing can have an essentially cuboid shape. The cupoid shape of the
housing can include a front narrow face and a rear narrow face, and upper
and lower longitudinal faces. An operating lever is provided on the front
narrow face for manual operation of the switching mechanism. The
short-circuit current release and the overcurrent release are connected
to the switching mechanism, which is arranged on the front narrow face.
The cuboid shape of the housing allows for the installation switching
device to be used in switchgear cabinets with 19-inch rack inserts.

[0022] With respect to the arrangement of the functional assemblies in the
interior of the housing of an installation switching device according to
the present disclosure, an exemplary embodiment provides that the
short-circuit current release and the overcurrent release are arranged
one behind the other in the housing, seen in the flow direction of the
current through the current path. This makes it possible to utilize the
space particularly well.

[0023] According to an exemplary embodiment of the present disclosure, the
first connecting point can be in the form of a connecting plate for
screwing to a contact rail. This arrangement allows the link to be made
to a copper rail in the switchgear cabinet.

[0024] According to an exemplary embodiment of the present disclosure, a
first coupling rod is provided for coupling the switching mechanism
operating element of the overcurrent release to the tripping lever. In an
exemplary embodiment, the switching mechanism operating element is
provided at its free end with a control cam body which has a control cam.
The first coupling rod, supported at a first end on the control cam, is
pressed by its second end against the tripping lever when the switching
mechanism operating element moves to the trip position. In this case, in
accordance with an exemplary embodiment of the present disclosure, the
switching mechanism operating element can be a shaft which is borne such
that it can rotate about its longitudinal axis. This allows force to be
transmitted efficiently between the overcurrent release directly to the
tripping lever. Since the magnetic overcurrent release has a rotating
shaft as the switching mechanism operating element according to an
exemplary embodiment of the present disclosure, the rotation of the shaft
is converted to a longitudinal forward movement of the coupling rod for
coupling to the switching mechanism.

[0025] The moments and forces which are created during this process can be
absorbed well by the housing without the sub-components being excessively
mechanically loaded.

[0026] According to an exemplary embodiment, the resetting force of a
first contact compression spring acts on the first contact lever in the
direction of the first stationary contact piece. The first contact
compression spring can be, for example, a contact compression spring
arrangement as described in the switching mechanism according to DE 10
2008 006 863 A1.

[0027] According to an exemplary embodiment of the present disclosure, the
second contact lever can be in the form of a moving contact link which is
provided with two moving contact pieces which interact with two
stationary contact pieces in order to form a double contact point. The
resetting force of a second contact compression spring acts on the second
contact lever in the direction of the stationary contact pieces. This
results in a double-contact point, which has the advantage that each
individual partial contact point is less severely loaded in the event of
short-circuit current disconnection than in the case of a single contact
point.

[0028] According to an exemplary embodiment of the present disclosure, a
second coupling rod is provided for coupling the moving contact link to
the striking lever of the switching mechanism. In this case, in one
advantageous aspect of the present disclosure, a linear movement of the
moving contact link during opening of the second contact point is
transmitted by means of the second coupling rod to a free end of the
striking lever, and causes the striking lever to pivot as a result. The
physical disconnection of the point at which the short-circuit current
release acts on the switching mechanism at the striking lever from the
point at which the overcurrent release acts on the switching mechanism on
the tripping lever has the advantage that this results in a design which
is flat overall and fits into a low housing with a low physical height of
44.45 mm, for example.

[0029] Further advantageous refinements and improvements of the present
disclosure are described below with reference to the drawings.

[0030]FIG. 1 shows a schematic view of an installation switching device 1
according to an exemplary embodiment of the present disclosure. In the
example of FIG. 1, the installation switching device 1 is illustrated as
a circuit breaker. The installation switching device 1 includes a housing
12. The housing 12 has an essentially cuboid shape, having a front narrow
face 15 and a rear narrow face 15', as well as an upper longitudinal face
17 and a lower longitudinal face 17'. An operating lever 16 is provided
on the front narrow face 15 for manual operation of the switching
mechanism 8, and the short-circuit current release 6 and the overcurrent
release 7 are connected to the switching mechanism 8, which is arranged
on the front narrow face 15.

[0031] The short-circuit current release 6 may be designed, for example,
as described in WO 2010/130414 A1. In addition, the overcurrent release 7
may operate, for example, as described in WO 2010/133346 A1. The
switching mechanism 8 may operate, for example, as described in DE 10
2008 006 863 A1.

[0032] A current path runs in the housing 12 between a first connecting
point 13 on the lower longitudinal face 17 and a second connecting point
14 on the rear narrow face 15'. The current path can be opened and closed
at a first contact point 4, which includes a first contact lever 5 as
well as a first stationary contact piece 2 and a first moving contact
piece 3.

[0033] The electromagnetic short-circuit current release 6 includes a
magnetic circuit with an air gap. The overcurrent release 7 includes a
switching mechanism operating element 48 which changes from a rest
position to a trip position when overcurrent tripping occurs. The
switching mechanism 8 includes a tripping lever 20 as well as a striking
lever 21 which can be pivoted between a rest position and a trip
position.

[0034] The current path includes a second contact point, in the form of a
double-contact point 4', 4'' with a second contact lever, also referred
to as a double-contact link 5'. The second contact lever 5' is arranged
at least partially in the air gap in the magnetic circuit such that, in
the event of a short circuit, an electrodynamic force which leads to
rapid opening of the second contact point 4', 4'' can act on the second
contact lever 5' as a result of the interaction of the current flow with
the magnetic flux within the air gap. The switching mechanism 8 acts via
a first operating connecting line 9 on the first contact lever 5 in order
to open the first contact point 4 and/or to keep it open. In the event of
overcurrent tripping, the overcurrent release 7 acts through the
switching mechanism 8 and via a second operating connecting line 10 on
the switching mechanism 8 in order to open the first contact point 4 and
keep it open. In the event of short-circuit tripping, the second contact
lever 5' acts via a third operating connecting line 11 on the switching
mechanism 8 in order to keep the first contact point 4 open.

[0035] The overcurrent release 7 is a magnetically active overcurrent
release, as described, for example, in WO 2010/133346 A1. A switching
mechanism operating element in the form of a shaft 48 which is borne such
that it can rotate about its longitudinal axis is formed thereon.
Furthermore, the overcurrent release 7 includes a setting element in the
form of a restraint spring, for example. In the event of an overcurrent,
the magnetic circuit of the overcurrent release exerts a torque on the
shaft 48 and attempts to rotate it in the clockwise direction. This
occurs only when the drive torque acting on the shaft 48 exceeds the
restraint torque exerted on the shaft 48 by the restraint spring. The
response threshold of the overcurrent release 7 is therefore adjustable.

[0036] A control cam body 51 is formed at the free end of the shaft 48.
This control cam body 51 is approximately in the form of a cylinder,
which is cut open in places at the side. A control cam is formed in the
control cam body 51. The first coupling rod 60 is supported at a first
end on the control cam. During rotation of the shaft 48, the control cam
ensures that the second end of the first coupling rod 60 is pressed
against the tripping lever 20, in order to unlatch the switching
mechanism 8 and to open the first contact point 4.

[0037] The rotary movement of the control cam body 51 with the control cam
is converted via the first coupling rod 60 to a linear movement, and the
switching mechanism 8 unlatches in the event of overcurrent tripping. The
first contact point 4 opens and interrupts the circuit.

[0038] In the event of short-circuit tripping, the contact link 5' opens,
and the switching mechanism 8 is unlatched via the coupling of the
short-circuit release 6 to the striking lever 21 by means of a second
coupling rod 39. The contact link 5' falls back to its original position
again, driven by the second contact compression spring 38', for example,
a leg spring, which acts on an attachment on the contact link 5', which
projects upwards from the magnetic release.

[0039] In the event of an overcurrent or short circuit, and during
switching during operation, the circuit is always disconnected via the
first contact point 4.

[0040] Connection is made to the copper rail 61, which can be a component
of a 19-inch rack insert, via the first connecting point 13. The device
is screwed to the copper rail 61 by means of a screw 62. The contact
between the copper rail 61 and the first connecting point 13 is provided
on the connecting face to the copper rail with a groove system, in order
to achieve a reliable contact. A braid 63 is welded onto the opposite
side in the housing, and is connected to the first contact lever 5.

[0041] The installation switching device described above can be used
particularly advantageously for protection of circuits using a low rated
voltage, for example of 60V, AC or DC, because no arc quenching device is
required since a short-circuit current is disconnected very quickly by
the electrodynamic short-circuit current release 6. Since the
anode-cathode voltage is already sufficiently great that it exceeds the
60V rated voltage such that the current is interrupted in this way, no
additional arc voltage is required in order to counteract the voltage
which is present at the terminals for disconnection. The installation
switching device described above can likewise be used advantageously in
applications where the ambient temperature fluctuates widely, because no
temperature compensation is required for the overcurrent release, because
the overcurrent release operates on a magnetic principle.

[0042] The present disclosure also includes any other desired combinations
of exemplary embodiments as well as individual refinement features or
developments, provided that these are not mutually contradictory.

[0043] Thus, it will be appreciated by those skilled in the art that the
present invention can be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
presently disclosed embodiments are therefore considered in all respects
to be illustrative and not restricted. The scope of the invention is
indicated by the appended claims rather than the foregoing description
and all changes that come within the meaning and range and equivalence
thereof are intended to be embraced therein.